This invention relates to a control apparatus for a vehicular battery-charging generator, and in particular to an apparatus for regulating the output voltage of a vehicular battery charging generator by controlling current flowing through the field coil of the charging generator.
This kind of a prior art vehicular charging generator from which this invention starts is shown in FIG. 1 wherein a generator 1 driven by an engine mounted on a vehicle (not shown) includes an armature coil 11, a field coil 12, a rectifier 13 which full-wave rectifies a three-phase alternating current generated from the armature coil 11 to provide a main output, and a rectifier 14 which is connected in parallel with the rectifier 13 and full-wave rectifies the main DC output of the rectifier 13 to provide a so-called "trio-voltage" output as an auxiliary DC output.
A voltage regulator 10 for regulating the main output voltage of the generator 1 to a predetermined value includes a power transistor 10a for controlling the field current of the field coil 12, a base resistor 10b disposed in the base circuit of the power transistor 10a, a transistor 10c for switchably controlling the power transistor 10a, voltage dividing resistors 10d and 10e serially connected to the trio-voltage output of the rectifier 14, a zener diode 10f as a voltage detecting device, for detecting the trio-voltage output of the rectifier 14, energized when the output voltage reaches or exceeds another predetermined value related to the above predetermined value, and a diode 10g as a surge absorber connected across the field coil 12. A battery 2 is connected across the rectifier 13 through a main conductor or wire 5 and charged by the generator 1 through the rectifier 13. An electrical load 3 for a vehicle is supplied with an electrical power from the generator 1 and the battery 2. A key switch 4 and a pilot lamp 20 for indicating "non-generation" state are serially connected to each other between the battery 2 and the regulator 10.
In operation, upon closing the key switch 4, a closed loop from the positive pole of the battery 2 through the key switch 4, the pilot lamp 20, the field coil 12, and the power transistor 10a to the negative pole of the battery 2 is formed whereby the field current is supplied for the field coil 12 of the generator 1 and simultaneously the pilot lamp 20 is lighted to indicate the "non-generation" state. In this state, when the engine is started, the generator 1 is driven to cause the rectifiers 13 and 14 to provide the respective output voltages corresponding to the rotational speed of the engine. As the output voltages of the recitifiers 13 and 14 approaches the terminal voltage of the battery 2 respectively, the voltage across the pilot lamp 20 decreases whereby the pilot lamp 20 is put out, oppositely indicating the fact that the generator 1 is under its normal operation i.e. power generation.
While the output voltages of the rectifiers 13 and 14 are lower than the predetermined value, that is the junction voltage of the voltage dividing resistors 10d and 10e is still lower than the above noted another predetermined voltage, the zener diode 10f is held to be non-conductive. As the rotational speed of the engine further increases and therefore the output voltages of the rectifiers 13 and 14 of the generator 1 become higher than the predetermined value, the junction voltage of the resistors 10d and 10e increases accordingly so that the zener diode 10f becomes now conductive, whereby a base current flows in the transistor 10c and through the zener diode 10f to make the transistor 10c conductive. In response to this, the power transistor 10a becomes non-conductive, thereby interrupting the field current of the field coil 12 to eliminate the output voltage of the generator 1.
When the output voltage of the generator 1 becomes lower than the predetermined voltage, the zener diodes 10f and the transistor 10c become non-conductive again so that the power transistor 10a is made conductive, which causes the field current in the field coil 12 to increase the output voltage of the generator 1 again. By the repetition of these operations, the output voltage of the generator 1 is regulated to the predetermined value which is typically about 14V.
In a prior art apparatus thus constructed, the generator 1 continues to hold a predetermined output voltage regardless of whether the vehicle is in its acceleration state or its deceleration state so that the engine is almost always loaded with the driving torque of the generator 1. Therefore, such a prior art apparatus is disadvantageous in that the acceleration/deceleration performance of the engine is worsened.
Moreover, although the power generator by the generator 1 is stopped to reduce the load on the engine during an unstable state such as the start of the engine, the battery 2 supplies an electrical power to various electrical loads during the stoppage of the power generation, and therefore the battery 2 may be over-discharged.
Furthermore, the pilot lamp 20 is inserted into a lighting circuit including the filed coil 12 and the power transistor 10a, so that the lighting circuit is not activated when the field coil 12 is disconnected or the power transistor 10a is broken, with the disadvantageous result that the pilot lamp 20 is not lighted even in the non-generation state.
On the other hand, Japanese Patent Application Laid-open No. 57-65230 discloses a control apparatus for a vehicular battery charging generator in which the rotational speed of the charging generator is detected to control the field current of the charging generator. Specifically, the rotational speed as detected is differentiated, and when the differentiated speed is higher than a positive predetermined value, the field current is reduced while when the differentiated speed is lower than a negative predetermined value, the field current is increased.